Spaces.
First of all, I like Python-like syntax (Python, Haskell) and tabs mess code very easily.
Tabs are:
1) of a different length in different environments and you can't control all of latter (skype, github, web, terminals, other text editors).
2) an archaic character originally designed for typewriters and re-purposed then into column alignment symbol for terminals (I think that tabs are good for formatting table columns in text mode) and then into indentation symbol for some reason unknown. I think if we want formatting, some more modern tools should be used. Why don't we use vertical tabulation and other weird control symbols from 70s?
2a) not minimalist. I can live without them (whereas I can't give up spaces), so why would I need it? I want plain text to be real plain text, without some formatting options living on their own.
3) my tools (square selection, smart indentation in vim) make work with spaces easy, they type spaces for me. When I'm forced to work with tabs, I also have to make additional explicit checks before every commit to make sure I haven't messed up anything.
4) I can adjust to an existing code style (thus far a style is good and consistent: 2/4/8 spaces is ok for me as far as that style is consistent), I don't have an urge to make it look like my own code every time.
tl;dr: don't try to make the world look as you want with tabs, adjust yourself to spaces!